I can create a table, change its colors, borders, left margin... but no matter what I tell it to do (either table width or margin-right) the right side of the table always extend until the border of what seems to be the content DIV.

I've tried HTML, I've tried CSS style in the table tag, I've tried putting the table in a DIV with a certain width...

It's like some higher power that I don't know off orders it to be so.

(I'm not an expert in HTML and CSS but I know a few things and I can read and copy-paste code...)

Any idea why it is this way (I'm interested, it's always good to learn) ?

The table won't fit in your main column because a) the contents are too wide at the default font-size and b) the theme specifies excessively large left and right padding for each cell. For starters, change the opening table tag from this:<table style="border:1px etc etc
to this:<table style="font-size:90%;border:1px etc etc

and change each opening td tag from this:<td>
to this:
<td style="padding:6px 10px;">`